refactor: reorganize models into subpackages

Move models into domain subpackages (max 4 files each):
- models/tool/ — tool_type, tool_instance, tool_definition_manifest
- models/config/ — config_profile
- models/user/ — user, user_config, ssh_key
- models/project/ — project, git_repository, workspace
- models/system/ — health_check, notification, instance_event, terminal_session

models/__init__.py continues to re-export all symbols, so consumers
using 'from src.models import X' are unaffected. Updated direct file
imports across the backend to use the new paths.

Quality gates: py_compile passed, ruff passed.

apps/api/src/models/config/__init__.py

@@ -0,0 +1,5 @@
+"""Config models module."""
+
+from src.models.config.config_profile import ConfigProfile, ConfigProfileInclude
+
+__all__ = ["ConfigProfile", "ConfigProfileInclude"]

apps/api/src/models/config/config_profile.py

@@ -0,0 +1,88 @@
+import uuid
+from typing import TYPE_CHECKING
+
+from sqlalchemy import (
+    Boolean,
+    ForeignKey,
+    JSON,
+    Integer,
+    String,
+    Text,
+    UniqueConstraint,
+)
+from sqlalchemy import Uuid as UUID
+from sqlalchemy.orm import Mapped, mapped_column, relationship
+
+from src.models.base import Base, TimestampMixin, UUIDPrimaryKeyMixin
+
+if TYPE_CHECKING:
+    from src.models.project import Project
+    from src.models import ToolType
+    from src.models.user import User
+
+
+class ConfigProfile(UUIDPrimaryKeyMixin, TimestampMixin, Base):
+    __tablename__ = "config_profiles"
+    __table_args__ = (
+        UniqueConstraint("user_id", "name", name="uq_config_profiles_user_name"),
+    )
+
+    user_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(), ForeignKey("users.id", ondelete="CASCADE"), nullable=False
+    )
+    name: Mapped[str] = mapped_column(String(255), nullable=False)
+    description: Mapped[str | None] = mapped_column(Text, nullable=True)
+    project_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(), ForeignKey("projects.id", ondelete="CASCADE"), nullable=True
+    )
+    tool_type_id: Mapped[uuid.UUID | None] = mapped_column(
+        UUID(), ForeignKey("tool_types.id", ondelete="CASCADE"), nullable=True
+    )
+    env_vars: Mapped[dict] = mapped_column(
+        JSON, default=dict, nullable=False
+    )  # {"VAR_NAME": "value", ...}
+    runtime_hints: Mapped[dict] = mapped_column(
+        JSON, default=dict, nullable=False
+    )  # {"start_command": "...", "working_dir": "...", ...}
+    mounts: Mapped[list] = mapped_column(
+        JSON, default=list, nullable=False
+    )  # [{"target": "/path", "mode": "rw", "files": {"rel/path": "content"}}, ...]
+    files: Mapped[dict] = mapped_column(
+        JSON, default=dict, nullable=False
+    )  # {"rel/path": "content", ...}
+    git_mounts: Mapped[list] = mapped_column(
+        JSON, default=list, nullable=False
+    )  # [{"remote_url": "https://github.com/user/repo.git", "source_path": ".", "target_path": "/path", "branch": "main"}, ...]
+    is_default: Mapped[bool] = mapped_column(Boolean, default=False, nullable=False)
+
+    user: Mapped["User"] = relationship()
+    project: Mapped["Project | None"] = relationship()
+    tool_type: Mapped["ToolType | None"] = relationship()
+    includes: Mapped[list["ConfigProfileInclude"]] = relationship(
+        "ConfigProfileInclude",
+        foreign_keys="ConfigProfileInclude.profile_id",
+        order_by="ConfigProfileInclude.order_index",
+        cascade="all, delete-orphan",
+    )
+
+
+class ConfigProfileInclude(UUIDPrimaryKeyMixin, TimestampMixin, Base):
+    __tablename__ = "config_profile_includes"
+
+    profile_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(), ForeignKey("config_profiles.id", ondelete="CASCADE"), nullable=False
+    )
+    included_profile_id: Mapped[uuid.UUID] = mapped_column(
+        UUID(), ForeignKey("config_profiles.id", ondelete="CASCADE"), nullable=False
+    )
+    order_index: Mapped[int] = mapped_column(Integer, nullable=False, default=0)
+
+    profile: Mapped["ConfigProfile"] = relationship(
+        "ConfigProfile",
+        foreign_keys=[profile_id],
+        back_populates="includes",
+    )
+    included_profile: Mapped["ConfigProfile"] = relationship(
+        "ConfigProfile",
+        foreign_keys=[included_profile_id],
+    )